What voltage is too low on 6v deep cycle system

[Sasq40]

Just wondering how low in voltage should I go before turning the Gen on?

Doing a test run camping with my invertor and my 2 deep cycle 6vs and don't know what my cut off voltage should be to keep the life good in my batteries.

[Skibane]

For a 12-volt battery bank (which includes having two 6-volt batteries connected in series), your batteries are going to be 70-80 percent discharged when the voltage drops below approx. 11.8 volts.

Discharging your batteries beyond approx. 80 percent will shorten their lifespan drastically.

(Some folks prefer to only discharge to 50 percent, in order to maximize the battery's lifespan. However, even at 80 percent discharge, a decent-quality battery will still deliver hundreds of charge/discharge cycles before it's worn out.)

Note that this voltage should be measured without any significant electrical loads on the batteries. With any sizable load present, all bets are off.

[bobphoenix]

On my 12V deep cycles, the alarm on my inverter goes off when the cell voltage reaches 1.75V, per cell... (per the instruction manual... Or 10.5V )
So, I would imagine it would be close to that for a three cell 6V as well... (4.5V)

[scrapperjohn]

12.1 volts is about 50% of battery on lead acid batteries.

[RRR]

Your two 6 volt batteries are likely wired in series to provide 12 volts. I generally fire up about 12.0 to 11.9.

The 12volt Side of Life (Part 1) Has info that is great.

[Old-Biscuit]

Voltage dropping into 'TAN' areas OK Occasionally

Voltage dropping into the "RED" areas........NO ---- will cause damage


Note: Estimating state of charge based on open circuit voltage is only accurate when batteries are at room temperature and have been resting — i.e. disconnected from all loads and chargers — for several hours.

[Sasq40]

I am indeed running then in series , I'll be sure to throw on the Gen when they hit 12-11.9

[Winemaker2]

Originally Posted by Skibane

For a 12-volt battery bank (which includes having two 6-volt batteries connected in series), your batteries are going to be 70-80 percent discharged when the voltage drops below approx. 11.8 volts.

Discharging your batteries beyond approx. 80 percent will shorten their lifespan drastically.

(Some folks prefer to only discharge to 50 percent, in order to maximize the battery's lifespan. However, even at 80 percent discharge, a decent-quality battery will still deliver hundreds of charge/discharge cycles before it's worn out.)

Note that this voltage should be measured without any significant electrical loads on the batteries. With any sizable load present, all bets are off.

Originally Posted by Sasq40

I am indeed running then in series , I'll be sure to throw on the Gen when they hit 12-11.9

Skibane is right on target and the problem with the plethora of charts many reference is the posters seem to never include the conditions that are NECESSARY to utilize the charts. And then there is the issue that many measure V and ignore the reqd conditions.
Many charts are built around resting V where no charge or load present for several hours... when folks are trying to decide DOD and the need tobstart recharge is when they need power vs when they can turn off all load for hrs to evaluate. It's a complex situation too many over simplify.
What I have found works best for us is to run gen during periods of high demand ( AM coffee & breakfast and evening meal prep) and let it run until SOC is back to a reasonable level to repeat the anticipated cycle.

The other factor many choose to ignore when recommending light DOD usage is you get many more cycles with low DOD but you use up many of those cycles recharging more often.

[Sasq40]

My goal is to try and not run the Gen unless we have to for something like ac. The only thing the invertor is really running is the beer fridge in the outside kitchen, we boil water for coffee and almost never use the microwave. If I could get 3-4 days on my batteries and not have to run the Gen would be ideal for us.

[SJ-Chris]

Originally Posted by Sasq40

The only thing the invertor is really running is the beer fridge in the outside kitchen

Depending what kind of fridge this is, it could eat up a TON of your battery capacity.

Originally Posted by Sasq40

If I could get 3-4 days on my batteries and not have to run the Gen would be ideal for us.

Time for some SOLAR! This can be very inexpensive to implement, especially if you just want to try it out (a portable system). You can start with buying 200-400w of used panels (...check craigslist or FB marketplace in your area) and an inexpensive charge controller and 40' of wiring. With this, you can implement a portable setup and you will keep that generator off almost indefinitely!


A while back I bought several 100w 12v used solar panels for $25 each (tested each prior to purchase). On Amazon, you could get an inexpensive PWM charge controller for ~$25, and 40' of 10 gauge wire for ~$40. 15amp inline fuse for ~$5. For less than $150 you can have 200w of portable solar keeping those batteries charged (and hopefully the beer cold) during the day. (I actually opted to use 300w and an MPPT charge controller and mounted them to the roof of one of my 23' Class C RVs that has two 6v batteries like you have...I haven't had any low voltage issues yet while boondocking).


Good luck!
Chris

[TacomaJoe]

As noted, those voltage charts are for a resting battery. Unless you lift the load and let the battery rest, you're working with bad data. The loaded voltage is a function of the load so that throws another wrench into the works.

I like a shunt meter to tell me how many amps I've pulled out of the battery. It's not an exact science because the battery capacity is a moving target but it beats measuring voltage to make the "when to charge" decision.

[Mark_K5LXP]

OldBiscuit's voltage charts are for open circuit, no load conditions. Not for when the batteries are being actively discharged, under load. Under load, the voltage is further diminished, and specified capacity (Ah rating) is realized down to 10.5V. Better than relying on terminal voltage to determine capacity, a shunt based battery monitor that counts amp hours is the way to go. Even the $20 ones work well enough to accurately indicate remaining capacity.

You *can* decide on any arbitrary point to fire off the genset and that's fine, but the higher you set it the more often you'll be on generator, so there's a compromise there on just what the point of having batteries is. There is a "sweet spot" between running on batteries and useful battery service life. Keeping them above 80% charged it would be impossible to realize all of their usable capacity, they'll die of old age before they're used up. Conversely, running them until dead every time will put you in a constant state of catch-up and no operating reserve. Depending on how you use them, whether you have infrequent high draws, more consistent low draws, or require a minimum operating time or duration of no generator will be the primary reasons you pick a particular discharge point to top off the charge. After that the battery service life is what it is, doing what you bought them to do. If you manage to use them up before they expire on their own, then *you win* - you got all the useful life you paid up front for.

Mark B.
Albuquerque, NM

[Sasq40]

According to my meter I have alot of time left, according to voltage not so much lol. these batteries are getting replaced when I get home, do figured run em hard to see what I use

[Sasq40]

Well that was also including my trucks battery's so good think I had my drill batteries to boost the old truck ha. Well need to Remeber to unplug from the truck next time